1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display device and luminance difference compensating method thereof.
2. Discussion of the Related Art
As the information-oriented society continually develops, the demand for display devices has risen in various forms. Many efforts have been made to research and develop various flat panel display devices including LCD (liquid crystal display), PDP (plasma display panel), ELD (electroluminescent display), VFD (vacuum fluorescent display) and the like. Some of the flat panel displays are already being used as displays in various instruments.
The LCD in particular has been widely used for mobile image displays to replace CRT (cathode ray tube) due to its advantages of being light in weight, slim in size, and low in power consumption. LCD is also being developed to be applicable to various fields for a TV monitor, a computer monitor, and the like to receive and display broadcast signals.
To be usable as a general display device, the LCD must be able to display an image with high definition and high luminance on a wide area while maintaining the advantageous characteristics of being light in weight, slim in size and low in power consumption.
The LCD generally includes a liquid crystal display panel for displaying an image thereon and a drive unit for applying drive signals to the liquid crystal display panel. The liquid crystal display panel typically includes a first glass substrate, a second glass substrate, and a liquid crystal layer injected between the first and second glass substrates.
The first glass substrate (or the thin-film-transistor (TFT) array substrate) includes a plurality of gate lines arranged in one direction and the gate lines are evenly spaced apart from each other. The first glass substrate also includes a plurality of data lines arranged in a direction perpendicular to the plurality of gate lines and the data lines are also evenly spaced apart from each other.
The intersections between the gate and data lines define a plurality of pixel areas. The first glass substrate also includes a plurality of pixel electrodes arranged in a matrix on the plurality of pixel areas and a plurality of thin film transistors are provided on the pixel areas to deliver signals of the data lines to the pixel electrodes. The data line signals are switched under the control of the signals of the gate lines.
The second glass substrate (or the color filter substrate) includes a black matrix layer to cut off light from areas other than the pixel areas, an RGB color filter layer to represent colors, and a common electrode. For In-Plane Switching (IPS) LCD, the common electrode is provided to the first glass substrate.
For the above-configured liquid crystal display device to be used as a display device with a wide area, a technology of assembling several liquid crystal display modules in a tile form has been proposed.
FIG. 1 illustrates a layout of a related art liquid crystal display device having a pair of tiled liquid crystal display modules and FIG. 2 is a cross-sectional diagram taken along a cutting line I-I′ in FIG. 1. The liquid crystal display device according to the related art includes a first LCD module 10, a second LCD module 11 attached to the first LCD module 10 in parallel, and first and second microlenses 20a and 20b attached to the first and second LCD modules 10 and 11, respectively. The first and second microlenses 20a and 20b compensate for a luminance variance due to a seam region S between the first and second LCD modules 10 and 11.
The first LCD module 10 includes an LCD panel 10a having upper and lower substrates, a backlight drive unit 10b provided under the LCD panel 10a to supply backlight, and a mold 13a for supporting and fixing the LCD panel 10a and the backlight drive unit 10b. Likewise, the second LCD module 11 includes an LCD panel 11a having upper and lower substrates, a backlight drive unit 11b provided under the LCD panel 11a, and a mold 13b for supporting and fixing the LCD panel 11a and the backlight drive unit 11b. 
FIG. 3 is a cross-sectional diagram for explaining light projection from the liquid crystal display device according to the related art. The LCD according to the related art is configured with the first and second LCD modules 10 and 11 and first and second microlenses 20a and 20b attached to the first and second LCD modules 10 and 11, respectively.
In this case, each LCD panel 10a, 10b is divided into an active area and an inactive area. Also, the seam region S exists between the first and second LCD modules 10 and 11.
To prevent the seam region S from appearing on a display screen, the light emitted from a peripheral region of each of the LCD panels 10a and 11a is diverted over the seam region S using the first and second microlenses 20a and 20b. 
Each microlens 20a, 20b includes a flat portion and a curved portion. The curved portions of the first and second microlenses 20a and 20b enlarge a portion of the image due to the distortion of the curved portions.
To compensate, the pixels of the LCD display are also divided to illuminate the corresponding flat and curved portions. A size of the pixels of the curved portion are designed to be smaller than a size of the pixels of the flat portion according to an enlarged ratio of the image distorted in the curved portions of the first and second microlenses 20a and 20b. 
Even though the image distortion can be minimized by designing the sizes of the pixels according to the curved and flat portions, a difference between opening ratios of the pixels occurs since the black matrix layer has the same width in both the flat and curved portions. As a result, a luminance difference occurs.
Due to the luminance difference occurring between the curved and flat portions of the first and second microlenses 20a and 20b, an overall luminance of a wide screen becomes irregular.